Manufacturing of an electrode structure exhibiting an excellent ohmic contact property is understood as an important technical issue in nitride semiconductor element such as semiconductor laser, light-emitting diode and so forth.
Patent Document 1 describes a semiconductor laser configured by providing, over a nitride semiconductor layer, an n-side electrode having a stacked structure composed of a plurality of metal layers. The n-side electrode of this semiconductor laser has a layer composed of Ti formed over the nitride semiconductor layer, a topmost layer composed of Au, and a Nb-containing layer provided between the layer composed of Ti and the topmost layer, as described in claim 1 of Patent Document 1, and is annealed together with the nitride semiconductor layer at a temperature of 400° C. or higher (600° C., for example).
The n-side electrode described in Patent Document 1 is aimed at obtaining a desirable ohmic contact between the layer composed of Ti and the nitride semiconductor layer.
According to Patent Document 1, the n-side electrode and an n-type GaN layer are annealed at a temperature of 400° C. or higher (600° C., for example) so as to expel hydrogen atoms intruded in the n-type GaN layer. It is described that, by expelling hydrogen atoms, a desirable ohmic contact may be established between the layer composed of Ti of the n-side electrode and the nitride semiconductor layer.
In addition, according to Patent Document 1, degradation of the ohmic contact is prevented by using the Nb-containing layer which prevents diffusion of Au towards the nitride semiconductor layer side, in the process of annealing. More specifically, in the electrode described in Patent Document 1, the Nb-containing layer functions as a barrier layer.
[Patent Document 1] Japanese Examined Patent No. 3239350